Frequency measuring system



Sept. 27, 1938. H. GRANGER FREQUENCY MEASURING SYSTEM Original FiledJuly 27, 1934 2 Sheets-Sheet 2 g Y M. v mi mg MN mm m 6 Maw OLW

TO NEXT DECHDE Patented Sept. 27, 1938 UNITED STATES FREQUENCY MEASURINGSYSTEM Harold Granger, Cherrydale, Va., assignor, by

mesne assignments, to Bendix Radio Corporation, New York, N. Y., acorporation of Dela- Ware Original application July 27, 1934, Serial No.

Divided and this application March 6, 1935, Serial No. 9,675

9 Claims.

My invention relates broadly to high frequency systems and moreparticularly to selective oscillator systems adapted to the measurementof the frequency of a given oscillation.

This application is a division of my copending application Serial Number737,309, filed July 27,

11934 for Selective high frequency oscillator sys- One of the objects ofmy invention is to provide a decade arrangement of frequency determiningelements in association with a plurality of oscillation circuits adaptedto measure the frequency of a given oscillation.

Another object of my invention is to provide a balanced mixer circuitfor combining two frequencies wherein the currents flowing at one of thefrequencies are opposed and cancelled in the output of the mixercircuit.

Still another object of my invention is to pro- 1 vide a system forchecking and determining the frequency of an electrical oscillation witha high degree of precision.

A further object of my invention is to provide an automatic arrangementwhereby the frequency I of an electrical oscillation may be measured anda permanent record made of such frequency.

A still further object of my invention is to measure the frequency of agiven oscillation by synthesizing a balancing frequency in successivedecade stages in accordance with the unknown gecade values of thefrequency in a given oscillaion.

Other and further objects of my invention reside in the circuits andarrangements more fully 35 disclosed in the specification hereinafterfollowing and in the accompanying drawings, in

which:

Figure 1 diagrammatically represents an arrangement of the decades offrequency determining elements for the measurement of a given frequency;and Fig. 2 is a schematic diagram of the connections in an automaticfrequency measuring and recording system embodying the circuits of myinvention.

My invention is directed to a compact construction of apparatus whichmay be conveniently transported and installed and which will simply andprecisely measure, indicate and record the frequency of an oscillation.The apparatus of my invention is particularly characterized by the widefrequency range over which the apparatus is designed to function.

' The apparatus of my invention employs a plurality of oscillatorcircuits, each controlled by a series of frequency determining elements.The elements in each series are productive of frequencies in the orderof an arithmetical progression, that is, the difference between thefrequencies of adjacent elements is the same, within a given series. Theseries of elements are further arranged so that the constant differencesin each series form a geometrical progression, that is, the constantdifferences of successive series are always in the same ratio. Thus, inthe arrangement shown, a decade system is adopted: that is, there areten elements in each series; the smallest constant difference is unity;and the constant differences forming the geometrical progression are 1,10, 100, and 1000, the constant ratio being :1.

In employing the arrangement shown in the measurement of an unknownfrequency, the thousands component of the unknown frequency is firstdetermined by balance with a selected 10- cal oscillation, the bestfrequency resulting being utilized in determining the hundredscomponent. Subsequently, the tens component is determined and finallythe units, thus precisely measuring the given frequency.

Referring to the drawings in more detail, Fig. 1 is a block diagram ofthe frequency measuring system of my invention designating certainfrequencies for the elements in each series which would form an operablecombination.

The units decade consists of an oscillator tube circuit associated withten piezo-electric crystals having natural vibration frequencies rangingfrom 150 kilocycles to 159 kilocycles in steps of 1 kilocycle. Any oneof these crystals may be connected to the oscillator tube by means of amanually operated switch having ten positions numbered from 0 to 9inclusive, the zero position connecting the 150 kilocycle crystal andthe 9 position connecting the 159 kilocycle crystal with theintermediate crystals connected to the corresponding successivepositions.

The tens decade, as shown in the block diagram, immediately above theunits decade, consists of an oscillator associated with tenpiezo-electric crystals having natural vibration frequencies rangingfrom 1350 kilocycles to 1440 kilocycles in steps of ten kilocycles. Anyone of these crystals may be selected and placed in the circuit foroperation in the same manner as accomplished in the units decade. Theten position switch is numbered from 0 to 9 inclusive, and the frequencycorresponding to each position is indicated in the block diagram.

The hundreds decade is similar to the units and tens decades except thatthe natural vibration frequencies of the crystals range from 3500kilocycles to 4400 kilocycles in steps of 100 kilocycles.

The frequencies of the crystals in the thousands decade unit aredetermined by the range desired in the system. In this case, as shown inthe block diagram, the thousands decade contains a thousand kilocyclecrystal and a two thousand kilocycle crystal.

Mixer circuits are provided to interconnect the various componentoscillations in the system.

, quency of 1535 kilocycles.

The thousands decade mixer combines the input oscillation of unknownfrequency and a selected oscillation from the thousands decadeoscillator and has a range of 1000 frequency units. The beat frequencyresulting is mixed with a selected frequency from the hundreds decade inthe hundreds decade mixer, which has a range of units, and the beatfrequency produced is Dased to the tens decade mixer, which has a rangeof 10 units, where it is combined with a selected frequency from thetens decade. The resulting frequency is matched as closely as possiblewith a frequency from the units decade. From the values of thefrequencies thus selected from the decade groups, the given frequency isknown, since an algebraic sum of the known component frequencies hassubstantially balanced the unknown frequency; that is, the circuits ofthe measuring arrangement have been made resonant to the unknownfrequency, said resonance being precisely controlled by selectedfrequency controlling elements in the several oscillator circuits in thesystem.

To measure a frequency between 3,000 and 7,999 kilocycles, a decadesystem with crystal frequencies and oscillators, as shown in Fig. 1,would be employed and could be embodied in either a manual or anautomatic system. Consider a frequency of 4135 kilocycles. In order thatthe hundreds decade transmit energy, it is necessary to secure a beatfrequency between the signal frequency, 4135 kilocycles, and somecrystal frequency of the thousands decade oscillator which would bebetween 5,000 and 5,999 kilocycles which is the range of the thousandsdecade mixer. The only crystal frequency of the thousands decadeoscillator which will give such a beat frequency is the thousandkilocycle crystal which, when using the sum frequency, will produce thebeat frequency of 5135 kilocycles. Referring again to the block diagramin Fig. 1, it is seen that when the 1,000 kilocycle crystal is in use inthe thousands decade, the crystal selector switch or decade switch is on4 or 6. The connection in this case is such that when the switch is oncontact 4, the sum frequency is delivered from the mixer circuit. Four,then, is the tap selected and 4,000 is the measurement given by thethousands decade. Next, it is necessary to mix a frequency with 5135kilocycles to produce a frequency between the limits of 1500 and 1599kilocycles, the tuning range of the hundreds decade mixer. 3600kilocycles, when mixed with 5135 kilocycles will produce a differencefre- 3600 kilocycles in the hundreds decade corresponds to l on thecrystal selector switch and thus, we have 4100 as the measurement by thethousands and the hundreds decades.

It is now necessary to mix a frequency with 1535 kilocycles to produce afrequency between the limits of and 159 kilocycles, the range of thetens decade mixer. 1380 kilocycles in the tens decade oscillator willproduce, when mixed with 1535 kilocycles, a difference frequency ofkilocycles. 1380 kilocycles corresponds to 3 on the decade switch in thetens decade and thus 3 is the third number in the measured frequency andwe have 4.130 as the measurement at this state. The 155 kilocycleoscillation is now mixed with a frequency from the units decade to produce the lowest audible beat note. In this case, the 155 kilocyclecrystal in the units decade corresponding to 5 on the decade switch willproduce a zero beat frequency and the original input frequency has beenmeasured as being 4135. While the Zero audio frequency cannot be heard,it is found at tap 5 between 1000 cycle notes on taps 4 and 6, 2000cycle notes on taps 3 and '7, etc., and is thus easily identified.

The system of my invention may be adapted for automatic operation tomeasure the frequency of an oscillation impressed on the system. Thevarious tap arrangements for selecting a particular frequencydetermining element for operation in the oscillator circuit and acorresponding tuned circuit cooperating therewith are adapted to beactuated by Strowger relays. A mixer circuit of the balanced rectifiertype is employed throughout the system. Such a mixer circuit is fullydescribed in detail in my copending application, Serial No. 737,309, ofwhich this application is a division. The tuning of the mixer circuit iseffected by tuning the input circult of the amplifier connected with theindividual mixer circuit.

As shown in. Fig. 2, I provide a motor I which rotates the tuningcondensers in each decade amplifier by means of friction clutches 2which may be disengaged magnetically. The motor also drives, througheach clutch, a cam arrangement 3 which operates contacts 4. Whencontacts 4 are closed, Strowger relay 5 is energized and operates toadvance the crystal selector switch and tuned circuit switch one tap.Condensers continue to rotate and tune through the range. If no beatfrequency Within the range of the tuning cycle is produced, the cam 3again operates contacts 4, and energizes relay 5 to advance the selectorswitches another tap. This operation takes place until a beat frequencyoccurs between the incoming signal from the radio frequency amplifierand the crystal frequency which is being used. At this position of thecondensers, there is an increase in the plate current in the amplifierwhich operates relay 6, releasing the friction clutch 2 and closingcontacts 6a and 6b. Contacts 6a supply plate potential to the nextamplifier and contacts 6b prepare Strowger relay '1 for operation.

The controls in the next decade continue to rotate and at eachrevolution advance the crystal selector and tuned circuit switches onetap until a beat frequency occurs. The relay 8 is then energized closingcontacts 8a and 8b. This interconnection extends to include controls ineach decade frequency unit.

In the arrangement shown in Fig. 2, the relay 8 is considered asconnected in the units decade control, that is, the final selectinggroup, and contacts 8a are not employed. Contacts 81) on the other hand,are used to actuate mechanism necessary to automatically print thefrequency measured on a tape to automatically record the frequency. Asshown in Fig. 2, Strowger relay 9 is connected in parallel with Strowgerrelay 5 so that the angular motion at 9 is equal to that at 5 and isemployed to rotate a drum 10 having on its periphery number dies 12corresponding to the numbers on manually operated decade switches, asshown in the block diagram of the decade frequency unit in Fig. 1. Leadsfrom Strowger relay coil 1 are shown to next printer, indicating thatthey would actuate another relay and mechanism identical with that at 9so that the number in the second frequency decade would be automaticallyprinted when the entire opera tion of measuring had been completed. Eachdecade frequency section is thus provided with a printer unit, and whencontacts 8b are closed,

relay I4 is energized, and actuates the arm 15 which prints the numbersaligned on the several drums on a tap l6. At the same time, relay l4also opens contacts I! opening the plate circuits of the severalamplifiers and returning the tuning mechanism to its original conditionwhere all controls are rotating.

In the manual system, the correct tuning to obtain the best frequency inthe range of the unit is indicated by the deflection of the needle inthe meter in the output circuit of the respective mixer. In theautomatic system, the relay in the output circuit automatically respondsto the increase of current at the position of correct tuning, orresonance.

While Figures 1 and 2 are diagrammatic, it is understood that theswitches shown in each decade will be controlled by dial or index meanson a panel, and digits corresponding to the digits shown in each decadein Figure 1 will be associated with the dial or index means in the samemanner as indicated in Figure 1. A suitable panel and dial arrangementis shown, for example, in Figure 7 of the copending application, SerialNo. 737,309, above referred to. While this panel arrangement is referredto as an example, it is to be understood, of course, that other paneland dial arrangements may be utilized. For example, a rotating dialmight bear thereon the digits and a fixed index might be used toindicate the correct digit in each decade. Other arrangements will, ofcourse, occur to those skilled in the art and it is therefore notintended to limit the dial indicating arrangement to any particularform.

I have shown my invention particularly adapted for operation with piezoelectric crystals, but I desire that it be understood that my inventionis equally adaptable to magnetostriction and other types of constantfrequency devices.

While I have described my invention in certain of its preferredembodiments, I desire it to be understood that modifications may be madeand that no limitations upon my invention are intended other than may beimposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. In a frequency measuring system the combination of a plurality ofoscillation generators, one of said oscillation generators includingmeans for producing a plurality of frequencies increasing in steps ofone thousand frequency units, a second of said oscillation generatorsincluding means for producing a plurality of frequencies increasing insteps of one hundred frequency units, a third of said oscillationgenerators including means for producing a plurality of frequenciesincreasing in steps of ten frequency units and a fourth of saidoscillation generators including means for producing a plurality offrequencies increasing in steps of one frequency unit, a mixer circuitfor said first generator, means for feeding oscillations of an unknownfrequency to said mixer circuit for producing a beat frequency betweenoscillations generated by said first generator and the unknown frequencyoscillations, and means for beating said heat frequency with a frequencyproduced by said second oscillation generator for producing a beatfrequency of lower frequency, and means for beating said last beatfrequency with a frequency produced by said third oscillation generatorfor producing a beat frequency of still lower frequency, means forbeating said last beat fourth oscillation generator for producing a substantially zero beat frequency, means for indicating said substantiallyzero beat frequency, means for determining the frequency of the unknownfrequency, automatic means for making a printed record of saiddetermined frequency, and means controlled in accordance with theadjustment of said oscillation generators and said mixer circuits forcontrolling said automatic printing means.

2. In a decade frequency measuring system the combination of a pluralityof oscillation generators, said oscillation generators being arranged ina series such that the first oscillation generator is adapted to producea plurality of frequencies increasing in steps of one thousand frequencyunits; an indicator dial for said first oscillation generator, saidindicator dial having a plurality of digits each corresponding to adifferent frequency generated, the second oscillation generator isadapted to produce a plurality of frequencies increasing in steps of onehundred frequency units; the third oscillation generator is adapted toproduce aplurality of frequencies increasing in steps of ten frequencyunits and the fourth oscillation generator is adapted to produce aplurality of frequencies increasing in steps of one frequency unit, anindicator dial for each of said second, third, and fourth oscillationgenerators, each of said last mentioned indicator dials having aplurality of digits thereon, each digit corresponding to a differentfrequency produced by the correspondng generator, means including amixer circuit connected to each generator for producing a unique beatfrequency between the oscillations derived from one of said oscillationgenerators and oscillations of an unknown frequency and means forproducing a series of unique beat frequencies of progressivelydecreasing frequencies between the outputs of each of said oscillationgenerators and the beat frequency derived from the mixer circuit of thepreceding generator for deriving a zero beat, means for indicating saidzero beat, the digits of said indicator dials being so arranged withrespect to the frequencies of said first, second, third, and fourthoscillation generators that the frequency of unknown frequencyoscillations is given by said indicator dials direct when said zero beatis indicated, by collecting the digits indicated by said dialscorresponding only to the frequencies of said oscillation generatorsused to obtain said zero beat.

3. In a decade frequency measuring system the combination of a pluralityof oscillation generators, one of said oscillation generators includingmeans for producing a plurality of frequencies increasing in steps ofone thousand frequency units, a second of said oscillation generatorsincluding means for producing a plurality of frequencies increasing insteps of one hundred frequency units, a third of said oscillationgenerators including means for producing a plurality of frequenciesincreasing in steps of ten frequency units and a fourth of saidoscillation generators including means for producing a plurality offrequencies increasing in steps of one frequency unit, a mixer circuitfor said first generator, means for feeding oscillations of an unknownfrequency to said mixer circuit for producing a unique beat frequencybetween oscillations generated by said first generator and the unknownfrequency oscillations, and means for beating said beat frequency with afrequency produced by said second oscillation generator forproducfrequency with a frequency produced by said ing a unique beatfrequency of .lower frequency, and means for beating said last beatfrequency with a frequency produced bysaid third oscillation generatorfor producing a unique beat frequency of still lower frequency, meansfor beating said. last beat frequency with a frequency produced by saidfourth oscillation generator for producing a substantially zero beatfrequency, means for indicating said substantially zero beat frequency,an indicator dial for each of said oscillationgenerators, each of saidindicators having a plurality of digits corresponding to the number offrequencies to be developed by the corresponding generator, the digitsof each of said indicators being so arranged with respect to each of thefrequencyv selectors of each of said first, second, third,.and fourthoscillation generators that the frequency of the unknown frequencyoscillations is given by said indicators direct when said zero beat isindicated, by collecting the digits indicated by said indicatorscorresponding only to the frequencies of said oscillation generatorsused to obtain said zero beat.

4. In a decade frequency measuring system the combination of a pluralityof oscillation generators, one of saidoscillation generators includingmeans for producing a plurality of frequencies increasing in steps ofone thousand frequency units, a second of said oscillation generatorsincluding means for producing a plurality of frequencies increasing insteps of one hundred frequency units, a third of said oscillationgenerators including means for producing a plurality of frequenciesincreasing in steps of ten frequency units, a fourth of said oscillationgenerators including means for producing a plurality of frequenciesincreasing in steps of one frequency unit, a mixer circuit for saidfirst generator, means for feeding oscillations of an unknown frequencyto said mixer circuit for producing a beat frequency betweenoscillations generated by said first generator and the unknown frequencyoscillations, and means for beating said beat frequency with a frequencyproduced by said second oscillation generator for producing a'beatfrequency of lower frequency, and means for beating said last beatfrequency with a frequency produced by said third oscillation generatorfor producing a beat frequency of still lower frequency, means forbeating said last beat frequency with a frequency produced by saidfourth oscillation generator for producing a substantially zero beatfrequency, means for indicating said substantially zero beat frequency,means for determining the frequency of the unknown frequency, said lastmentioned means including an indicator for each of said oscillationgenerators, each of said indicators having a plurality of digitscorresponding to the number of frequencies to be developed-by thecorresponding generator, the digits of each of said indicators being soarranged with respect to each of the frequency selectors of each of saidfirst, second, third, and fourth oscillation generators that thefrequency of the unknown frequency oscillations is given by saidindicators direct when said zero beat is indicated, by collecting thedigits indicated by said indicators corresponding only to thefrequencies of said oscillation generators used to obtain said zerobeat, automatic means for making a printed rec- 0rd of said determinedfrequency, and means controlled in accordance with the adjustment ofsaid oscillation generators and said mixer circuits for controlling saidautomatic printing means.

'5. In a decade, frequency measuring system the combination of anoscillation generator system having four sets of electromechanicallyvibratile standard frequency elements, frequencies of the elements ofeach of said sets being arranged to increase progressively bypredetermined steps, an indicator device for each of said sets ofelectromechanically vibratile elements, each of said indicator deviceshaving a plurality of digits thereon, each of said digits correspondingto a frequency step, means for deriving a frequency fromsaid'oscillation generator system and producing a Zero beat with anunknown frequency, the digits on saidindicators being so arranged withrespect to the frequencies of said first, second, third, and fourth setsof relectromechanically vibratile elements that the value of the unknownfrequency is given direct by said indicators when said Zero beat isproduced.

6. A decade frequency measuring system according to claim 5 including,automatic means for making a printed record of the given value of theunknown frequency and means connected to selected ones of saidoscillation generators for controlling said automatic printing means.

7. A decade frequency measuring system according to claim 2 includingautomatic means for making a printed record of the frequency given bysaid indicators and means controlled in accordance with the adjustmentof said oscillation generators and said mixer circuits for controllingsaid automatic printing means.

8. In a system for measuring oscillations of unknown frequencies, aplurality of series of electromechanical vibratory oscillationgenerators, each series having a predetermined frequency relation toeach of the other of said series, means for producing a beat frequencybetween only one generator in any one series and an oscillation ofunknown frequency, means for combining the beat frequencies of two ormore of said series, the several generators in each of said series beingrepresented by digits which are repeated in each of said series,indicating means associated with each of said series whereby when zerobeat is: obtained between the last of said series and said oscillationof unknown frequency the digits indicated by said indicating means willgive a direct reading of the value of said oscillation of unknownfrequency.

9. In a frequency measuring system, a plurality of oscillator decades,the oscillator frequencies in each decade being separated by a constantamount, the several decades of the series being separated in frequencyby a constant ratio, mounting means for said decades bearing asuccession of the same digits for each decade, oscillator mixingcircuits interconnecting the several decades and an oscillator of afrequency to be determined, means for causing a unique beat frequencysuccessively between said decades and the last mentioned oscillator,indicating means associated with each of said decades, said indicatingmeans cooperating with digits of said decades to give a direct readingof the value of the frequency originally to be determined.

HAROLD GRANGER.

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